Muscle Contraction Signaling Pathway

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Questions and Answers

What is a key difference between smooth muscle and skeletal muscle contractions?

Skeletal muscles respond to a variety of stimuli, while smooth muscles only respond to excitatory stimuli

Smooth muscles contract faster than skeletal muscles

Skeletal muscles create more tension over a long period of time (correct)

Smooth muscles lack striations, while skeletal muscles have z lines

Where is actin bound in smooth muscles and what does it anchor to?

Actin is bound to dense bodies and anchors to extracellular fluid (correct)

Actin is bound to z lines and anchors to the sarcoplasmic reticulum

Actin is bound to troponin and anchors to the ECF

Actin is bound to myosin and anchors to the cytoplasm

How are neurons connected to smooth muscles compared to skeletal muscles?

Neurons in smooth muscles form neuromuscular junctions with muscle fibers

Neurons in smooth muscles are directly connected to each muscle fiber

Neurons in smooth muscles are not directly connected like in skeletal muscles (correct)

Neurons in skeletal muscles do not influence muscle contractions

Why do autonomic nerves connect to smooth muscles instead of somatic nerves?

Autonomic nerves can control involuntary functions like smooth muscle contractions Signup and view all the answers

What is a distinguishing feature of autonomic neurons at the junction of smooth muscles?

They can modulate the strength and speed of muscle contractions in smooth muscles Signup and view all the answers

What is the neurotransmitter released by autonomic nerves?

Norepinephrine Signup and view all the answers

Which system is associated with norepinephrine?

Sympathetic Signup and view all the answers

What type of muscle undergoes mitosis and hyperplasia?

Smooth muscle Signup and view all the answers

What is the purpose of the circular arrangement of smooth muscle in the viscera?

Controls lumen size Signup and view all the answers

Which type of smooth muscle can contract as a unit due to gap junctions?

Single unit smooth muscles Signup and view all the answers

How can calcium concentration decrease in a smooth muscle cell?

Via a second messenger IP3 pathway Signup and view all the answers

Which of the following is a direct effect of parasympathetic innervation?

Stimulating saliva production Signup and view all the answers

Where is the primary concentration of sympathetic innervation?

Sympathetic trunk Signup and view all the answers

Which type of cholinergic receptor is classified as second messengers?

Muscarinic receptors Signup and view all the answers

What is the primary action of alpha 2 adrenergic receptors?

Inhibited release of catecholamines Signup and view all the answers

What is the primary neurotransmitter that alpha 1 adrenergic receptors respond to?

Norepinephrine Signup and view all the answers

Which drugs are commonly used to block beta 1 adrenergic receptors?

'Metoprolol' Signup and view all the answers

What is the triad of symptoms associated with Horner’s syndrome?

'Ptosis, miosis, anhidrosis' Signup and view all the answers

How is acetylcholine removed from a synaptic cleft?

Hydrolyzed by acetylcholinesterase Signup and view all the answers

What is the primary role of beta 1 adrenergic receptors?

Increasing heart rate and contractility Signup and view all the answers

What is the role of Ca-Calmoudilin in smooth muscle contraction?

Forms a complex with myosin light chain kinase Signup and view all the answers

In smooth muscle contraction, what is the significance of myosin ATPase?

Cleaves ATP into ADP and Pi Signup and view all the answers

What factor contributes to maintaining a long period of tension in smooth muscle contraction?

Latch bridge mechanism Signup and view all the answers

Which neurotransmitter is released from the adrenal glands during adrenal innervation?

Epinephrine (EP) Signup and view all the answers

What is the main function of postganglionic fibers in the autonomic nervous system?

Conduction of nerve impulses away from ganglia Signup and view all the answers

In sympathetic innervation, where does acetylcholine (ACH) get released instead of Epinephrine (EP) and Norepinephrine (NE)?

Sweat gland innervation Signup and view all the answers

What is the main neurotransmitter released from the presynaptic neuron in a typical neuron?

Acetylcholine (ACH) Signup and view all the answers

What is the function of phosphatase in smooth muscle contraction?

Removes Pi from myosin Signup and view all the answers

Study Notes

Smooth Muscle vs. Skeletal Muscle

Lack striations, less myosin, no troponin (calmodulin)
Dense bodies instead of Z lines
Involuntary, responds to stretch, chemicals, temperature
Ca2+ from ECF, less developed SR
Slow, sustained contractions

Characteristics of Smooth Muscle

Actin bound to dense bodies, anchored to ECF and other smooth muscles
Creates work through contraction
Located in vessels (tunica media)
Not directly connected to neurons, no neuromuscular junction
Innervated by autonomic nerves (not somatic)
Autonomic neurons contain varicosities (swellings with NT storage)
Release norepinephrine and acetylcholine

Types of Smooth Muscle

Multi-unit smooth muscle:
- Can have own autonomic nerve connection
- Does not fire spontaneously
- Does not contract in response to stretch
Single-unit smooth muscle:
- Contains gap junctions
- Contracts as a unit (AP propagates from cell to cell)
- Can be spontaneously active (fluctuating threshold potential)
- Stretch can induce contraction

Stimulating Smooth Muscle

Autonomic nerves (excite or inhibit)
Chemicals (hormones, CO2, O2, NO, low pH, temperature, stretch)
Ca2+ concentration increase:
- "Leak channel"
- Voltage-gated channel
- Ligand-gated channel
- Stretch-activated channel
- IP3 pathway
- Calcium-induced calcium release
Ca2+ concentration decrease:
- Ca ATPase out of the cell
- Ca ATPase into the SR
- Ca2+/Na+ countertransporter

Smooth Muscle Contraction Pathway

Ca2+ enters via Ca2+ channels
Ca2+ binds to calmodulin to form Ca-calmodulin
Ca-calmodulin activates myosin light chain kinase (Ca-calmodulin MLCK) complex
Phosphorylates light chain on myosin head (1) and activates myosin ATPase
Myosin heads bind to actin and pull actin back toward its tail
Actin pulls on dense bodies and the cell contracts
ATP comes back and removes the myosin head from actin and resets the cross-bridge cycle

Phasic Contraction and Tonic Contraction

Phasic contraction: similar to skeletal muscle contraction
Tonic contraction (latch bridge mechanism):
- Myosin head binds to actin and waits for ATP to come in and remove myosin head
- Phosphatase comes in and cleaves Pi, leaving myosin head bound to actin without Pi
- ATP has lessened affinity to bind and remove myosin head, maintaining tension

Autonomic Nervous System (ANS)

Visceral efferent motor
Innervates smooth muscle, cardiac muscle, and glands
Sympathetic and parasympathetic divisions
Sympathetic: "fight or flight" response
Parasympathetic: "rest and digest" response
Both divisions work in tandem, never fully turning off or on

Sympathetic and Parasympathetic Innervation

Sympathetic:
- Preganglionic neurons: T1-T12 and upper 2-3 segments of the spinal cord
- Postganglionic neurons: short, unmyelinated
- Receptors: alpha and beta adrenergic
Parasympathetic:
- Preganglionic neurons: cranial nerves 3, 7, 9, and 10, and sacral portion of the spinal cord
- Postganglionic neurons: long, unmyelinated
- Receptors: muscarinic and nicotinic cholinergic

Adrenergic and Cholinergic Receptors

Adrenergic receptors respond to norepinephrine (NE) or epinephrine (EPI)
Alpha and beta receptors:
- Alpha 1: smooth muscle, visceral organs (GI tract), vasoconstriction
- Alpha 2: presynaptic, inhibits NE release
- Beta 1: heart, increases rate and contractility
- Beta 2: respiratory, uterine, and GI smooth muscle, vasodilation
Cholinergic receptors respond to acetylcholine (ACH)
Muscarinic and nicotinic receptors:
- Muscarinic: second messenger
- Nicotinic: ligand-gated

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Description

Test your knowledge on the signaling pathway involved in muscle contraction, from Ca+ entering via channels to myosin heads binding to actin. Identify the sequence of events leading to the contraction of muscle cells.